WASHINGTON, May 23 (Reuters) - Killer heat fueled by climatechange could cause an additional 150,000 deaths this century inthe biggest U.S. cities if no steps are taken to curb carbonemissions and improve emergency services, according to a newreport.

The three cities with the highest projected heat death tollsare Louisville, with an estimated 19,000 heat-related fatalitiesby 2099; Detroit, with 17,900, and Cleveland, with 16,600, theNatural Resources Defense Council found in its analysis ofpeer-reviewed data, released on Wednesday.

Concentrated populations of poor people without access toair conditioning are expected to contribute to the rising deathtolls.

June, July and August are expected to see above-normaltemperatures over most of the contiguous United States, frominland California to New Jersey, and from as far north as Idahoand Wyoming to Texas, Florida and the desert Southwest, theNational Oceanic and Atmospheric Administration said in a May 17forecast.

The last 12 months, from May 2011 to April 2012, were thewarmest in the contiguous United States since modernrecord-keeping began; last month was the hottest April on recordfor the Northern Hemisphere.

These figures show climate change is already beingpowerfully felt, and more dangerously hot summer days are inprospect under a business-as-usual scenario, said Dan Lashof,director of NRDC's climate and clean air program.

NRDC, which with other environmental groups has pushed forcurbs on U.S. emissions of heat-trapping carbon dioxide, isbacking a plan by the U.S. Environmental Protection Agency tolimit carbon emissions from new U.S. power plants. The EPA isholding public hearings on Thursday on the dangers of carbonpollution from power plants. The EPA's plan is unlikely to gointo effect until after this year's election campaign.

DEADLIEST DAYS

The deadliest days are those designated Excessive HeatEvents (EHEs), often in urban areas where air conditioning isscarce or unreliable, with sizable poor populations andmunicipal services unprepared for large numbers of peoplesickened by the heat, Larry Kalkstein, a University of Miamiprofessor who wrote two studies on the subject.

One was published in the American Meteorological Society'sjournal Weather, Climate and Society; the other in the journalNatural Hazards. Both were peer-reviewed.

There could be five times the number of Excessive Heat Eventdays by mid-century and eight times that number by the end ofthe century, Kalkstein said in a telephone briefing. The currentaverage number of EHEs per year is 233; by mid-century it couldbe 1,342, and by 2100, it could be 1,913.

The full report is available online at http://www.nrdc.org/globalwarming/killer-heat/ .

The most disastrous heat waves, like the one that killedmore than 700 people in the Chicago area in 1995, come when highheat lasts beyond two days in urban areas without plans to reachthe most vulnerable populations: the elderly, the obese andthose on medication.

Kalkstein praised Chicago for improving its heat warningsystem, emergency services and cooling centers since then. Healso said Philadelphia and Seattle had put measures in place tolessen the risk from excessive heat days.

The studies considered cities because that is wheretwo-thirds of the U.S. population lives, Lashof said. There issome evidence that heat deaths in rural areas will also rise,but that is harder to document, he said.

U.S. cities aren't the only ones bracing for the impacts ofextreme weather. Ten Asian cities are assessing how ready theyare to deal with floods, droughts, heat waves and other expectedresults of climate change.

The Asian Cities Climate Change Resilience Network isworking in 10 cities in India, Indonesia, Thailand and Vietnamto figure out technical indicators -- such as the capacity ofwater systems, sewage and waste-water services and the size ofdeforested areas upstream from urban areas -- to help plan toprotect city residents. More information on the plan isavailable at http://www.acccrn.org/ .